


It Started with Pranks

by LazySintastic13 (EmeraldWriter)



Category: Undertale (Video Game)
Genre: Alternate Universe - Underfell, Bara Sans, M/M, Prank Wars, Underfell Sans, kustard - Freeform
Language: English
Status: Completed
Published: 2018-06-24
Updated: 2018-06-24
Packaged: 2019-05-27 17:22:02
Rating: Teen And Up Audiences
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 3,673
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/15029477
Author URL: https://archiveofourown.org/users/EmeraldWriter/pseuds/LazySintastic13
Summary: It was a start of a war no one asked for.Prank after prank after prank.Something was bound to go wrong with one of them.And it did.





	It Started with Pranks

**Author's Note:**

  * For [silverryu25](https://archiveofourown.org/users/silverryu25/gifts).



> Another giftfic for ryu!~ XD

Red grinned evilly when he placed the plastic cup of green goo inside the refrigerator to cool. “Yo, Alph, borrowing the fridge for something.”

The aforementioned monster couldn’t help but role her eyes. “Is this for another prank? Are you and Sans still doing the prank war thing?”

“I’ll have you know, it’s  _always_  been our thing.” Red shrugged as he turned to leave. “And let me remind ya again that it was Sans who started it all.”

They met at work, just two new recruited scientists for the job. And they were to be partners too as they had applied for the same field of interest.

“Wow, looks like we’ll be seeing each other a lot.” Sans started up the conversation and raised his hand out for a handshake. “It’ll be nice working with ya.”

Red had been  _amiable_  enough to comply and returned the gesture. But what befell after would  _shock_  him. Literally.

The skeleton sneered when he saw the smug look on Sans’ face.  _Oh no, I ain’t going down like this you punk._

And it was a start of a war no one asked for.

From setting up multiple alarm clocks in the break room when the other was sleeping, changing the ink cartridge of a pen to a party popper, filling one’s cubicle with paper cups filled with water littered  _everywhere_ , messing with the key for the rooms by adding useless keys in the key ring, and so,  _so_  much more.

It felt endless. But they also had a system.

Each would get a turn at each other without fail. Didn’t matter the time or place, but there was also the bottom-line that the prank shouldn’t really hurt the other.

Because that’s what they really were. Playful pranks. 

And both skeletons had never met another so committed in keeping up the game. It brought excitement, and there was always something to look forward to.

But it doesn’t happen every day.

There are also times when they would relax, grab a coffee and just talk about nothing in particular. Moments where they would ask the other to eat out. Moments were one or maybe both, would come to realize how well they worked together.

Until they’ve become close before they realized it; closer than they’ve expected with each other—enough to disclose personal fears and troubles and getting the advice and comfort from the other.

There was something between them. From colleagues to friends to partners to ... best friends.

Because that’s where they currently sat. They grew to become best friends, and it was especially this bond that brought about fear in both of them, unbeknownst that the other felt the same way.

It was harder and more nerve-wrecking than everyone thinks when it came to the thought about crossing that line. Would they still stay the same? Would things become different? Does he feel the same?

What did it mean to cross that line?

Red never broached the subject. And he knew that Sans must’ve realized it as well for they never talked about it. Always ignored it. Always kept in a dark place as if it were a dirty secret.

But the tension was thick and present. Anyone who cared to notice would realize as well. But it was never to be spoken or acknowledged.

Not because Sans was afraid. No.

The skeleton had done nothing but be sweet and compliant in not discussing the subject, but it didn’t mean that he’d stop trying to take Red out on their ‘friend’ dates, and continue on with their little prank war.

No. It was all because of Red. Because the very idea scared him shitless. He likes what they have going on now, and he knows how greedy and selfish he was for doing so. Feeling as if he had been leading Sans on for nothing than just for shits and giggles.

But that wasn’t it! That was never the case.

Red just have ... been woken up from naïveté.

He had been so gullible then. And it was he who had been led on, been used.

When it had been his first relationship, he had cared so much and fallen so deep. He couldn’t see how poisonous the other truly was. And it was bad. So bad that his younger brother got involved in the whole drama of shitfest and hell ensued.

It was a hard recovery from there, but he still tried for the second time. That time, the monster that approached was sweet and gentle, and never did anything to push Red to take it any further.

He thought it was okay then ... but he was wrong for the second time. He would never have known that the fucker had been cheating on him with several monsters. And the worst part of it all, was that he was just a fling. Just another fling.

And he was sick of it. It was all so sickening. It hurt to love, and it hurt even more to continue loving.

So he stopped.

But that’s a joke in and of itself.

Because his soul always throbbed when Sans was around. As if he could truly feel the flutter of metaphorical butterflies in his stomach. As if his soul swelled in joy whenever he saw that cute smile.

As if he was...

It was nothing. It must be nothing.

And thus, the two skeletons continued their days this way.

* * *

 When Red left the lab, Alphys had placed an _identical_ cup beside the one Red had set to its left. 

But upon closing the fridge, she realized that she should label which one was hers.

So grabbing a marker, she went back to the fridge, and took the cup on the _right_ to label as hers.

Satisfied, she placed it back in and decided to pack up and go home.

* * *

 It was the next day, and Red had long since prepared his little prank.

He had grabbed the cup that didn’t have a label, and began to mix it in more goo fluids so that he’d have a bucket full; he made it a little watery so that it would drip all over Sans easier and not be to viscous.

Once Sans sat on his seat, he’ll trigger the whoopie cushion button and thus have his mechanism swing the bucket to soak him. It was perfect.

And all Red needed to do was wait.

Currently, after having it all up, he was in the break room minding his business. He already had the camera set so that he didn’t need to be there to take a picture.

Red snickered, just imagining the disgusted look of being covered in goo. Hehe, it was going to be priceless.

Five minutes of waiting was all it took before Red heard the loud cussing through the walls. And it wasn’t long before Sans ported in, looking like a slime monster.

“Oh, is that a new look you’re trying out?”

Sans’ mouth twitched. “I don’t think green is quite my colour.”

“Well, it ain’t mine.” Red continued to smile as Sans ignored him to wipe off the mess with a towel from his locker. He definitely needed a shower.

The two skeletons jumped when the door suddenly slammed open, and in came Alphys, panting heavily.

“R-Red, the cup without my na—”but she cut herself off when she realized that Sans was covered in the green fluids. “Oh no! Sans you go and rinse quickly! I l-labelled wrong and Red and I’s cup switched. You’re currently drenched in one of the vials for my experiment.”

Hearing this had both skeleton’s eyes widen, and Sans immediately ported out whilst Red stood to ask Alphys for the details.

“I’m sorry. I’m not sure of the effects since it was just recently made and not been tested yet. Through hypothetical research; however, it’s only supposed to stimulate hormones, but to what level and how, as in, if it would make the subject inhibit or exhibit aggression, instincts, body growth, and the like, I’m really not sure.”

Red cursed as his heart shook with worry. He hoped that the vial showed no effects and became a flop. Maybe it wasn’t even susceptible to monsters or monster skeletons specifically?

Red didn’t know, but stars he hoped Sans was really okay.

He waited in the break room for Sans, and the latter came back fifteen minutes later. Red stood up immediately. “Are you okay? Feeling weird anywhere? Feeling strange? Are you dying? Oh stars I’m so sorry. I didn’t know. If only I checked and then you wou—”

“Red, I’m okay.” Sans smiled gently and went to hug his panicking partner. “I think I managed to wash it off fast enough that it didn’t have any effect.”

Red returned the embrace and sighed in relief. “Good. That’s good.” He rested his head on the other’s shoulder. “... ‘m sorry.”

Sans chuckled. “It’s fine. I know you didn’t mean to.” The skeleton in his hold simply hummed. “It’s okay Red.” He leaned back and suggested. “Say, why don’t we just take a day off today and go watch a movie together? I heard that new action movie starts screening today.”

Red looked at Sans, observing for anything that may look different. And seeing nothing only then did Red relaxed and nodded. “Sounds good.”

They headed to the elevator, because while their magic worked, there was a barrier in each floor so that leaked out experiments won’t affect the other floors. As such, Sans had merely ported to the shower rooms in which each floor has five of them. So the elevator was their only option.

But who would’ve thought that there would be a power shut down after Sans and Red had only gone down three floors in. They needed to head to the lobby which was at least nine more floors away. And now they were stuck. Only the power was out, so the magic barrier was still active. Much to both skeletons’ dismay. Because it meant that they had to wait it out.

“Fuck, are you fucking kidding me?”

Sans chuckled, “Well, looks like we’ll just have ... linner?”

Red snorted. “More like dunch.”

That got Sans cracking up. “It–snnrk–has to be duncher.”

Laughter filled the dark elevator room. Both skeletons decided to just sit it out and talk about nothing in particular like the usual.

Suddenly, Sans lurched in pain, clutching his chest tight as he began to pant heavily. He was also sweating profusely and feeling very hot; his eye lights began to flare with magic and his rib cage glowed beneath his clothes, illuminating part of the room.

Red was startled and eyes widened at the magic influx. “Sans! Wha—”

_“Stay away!”_

The sudden drop of an octave made Red jump, and his mouth gaped in terror in seeing Sans’ bones enlarge; ripping the shirt in the process, and the shorts managed to survive. “O-Oh fuck. S-Sans! You’re—”

Red was cut off when Sans _howled_ in pain, the magic still whirling erratically inside.

“Sa—”

“S’ _fine.”_ The large skeleton panted, doing his damnest to keep it under control. If he so much as let go, his magic may lash out and gravely hurt Red. “Stay—” _there_. He couldn’t continue, shutting his eyes to concentrate on his task at hand.

Red felt his soul twinge in pain. He was the cause of this. Because of that sample. And even if he wanted to help, what could he really do?

Red had no other choice but to trust that Sans had it under control. So he stood in place, waiting and watching. The worry engulfed his core in waves.

He didn’t know how much time had passed. What was only minutes felt like hours. And he saw Sans’ magic finally becoming stable.

But now he...

Red called out. “Sans? You still okay there?”

Sans attempted to calm his nerves by taking deep breaths, his scrunched eyes opening slowly. “... ‘M fine.” He muttered before leaning back on the wall to rest.

The small skeleton looked at his friend in both awe and fear. Sans was fucking huge. Like, what-the-fuck huge. But he was also really concerned of the other’s well-being. Such a ... growth spurt would no doubt have hurt from the screams the other let out. So he asked, “Can I ... come to you?” He wanted to inspect for any wounds or problems on Sans’ body. And hearing a grunt, Red rushed over.

His small hands patted and moved thick and heavy bones. Then Red climbed on Sans’ lap, standing to inspect the chest for any problems.

Red let out a sigh of relief when there were no injuries or marks. Then he recalled what Alphys said. Stimulate hormones for growth? Check. Aggression? 

Red tiptoed to tap Sans’ face, blues meeting with bright reds. “You angry at me?”

Sans gave Red a confused look but still answered. “No.”

No aggression then ... How to test instincts though? 

While Red was thinking of a way, Sans stared at the small skeleton in front him. His soul pulsed quick, thrumming with joy; as it always did every time Red was around.

“You’re amazing.” The words left before Sans bothered to think about it. It was just ... something he’d always wanted to say.

Red was taken out his reverie from the words, and looked up at Sans. “Wha—”

“And so beautiful.”

The small skeleton’s face flushed. Embarrassment welled up inside along with confusion. Just what the hell was Sans spouting about?!

“You’re really smart, and funny. I always looked forward to what you’ll do. How you’d get back at me.”

Seeing the pure admiration and something else that Red refused to identify, it hit him that this was simply Sans telling him of his unscreened and unconcealed thoughts. And to be honest, he didn’t know what to really think of it.

“You know, I asked Fell about you.”

Red raised a brow, “My brother?” Apparently, this also meant that Sans was going to be more candour with him.

Sans hummed. “I asked for his permission. If it was okay to date you.” Red’s breath hitched, his small hands unconsciously trembling. “He made me do a lot of tests. And made me answer a lot of questions. Even about my sex life and previous partners.”

While Red was thankful and happy about his brother’s care, it was also a little embarrassing how invasive his brother was. Sans must’ve been really uncomfortable and felt very awkward.

“I didn’t mind you know? If it meant I can have a chance with you.”

Red’s soul twisted at the words. And more so when he saw the sudden sorrow in the other’s eyes.

“But I know that you don’t even like me that way.” Red gripped at the thick bones of the other’s chest, wanting to say something but ended up feeling that he couldn’t. “I’m fine with what we have. I don’t want to lose being your friend because I was being selfish.”

 _No! You’re wrong. I..._ Red wanted to scream it, but still he said nothing. His soul thumped hard against his chest, knowing where it was going. And he can’t bear to hear it.

“It’s not even your fault that I—”

 _No! don’t say it! You ca—_  
  
—Fell in love with you, Red.”

The small skeleton closed his eyes, the hot tears sliding down his cheeks. His whole body shook as the surge of emotions whirled inside.

He said it ... This was what Sans thought.

Red didn’t know what he should do.

Was he ... ready to try again? Was it too soon?

Red even used the excuse that Sans was simply being under the influence of the sample, that he didn’t really know what he was saying. But that was just it wasn’t it.

This was what Sans truly felt.

And Red felt like a scum for trying to cover it up, as if it were filth.

Seeing Red cry, Sans’ heart tightened, as if prickled with thorns. No. He didn’t want Red to cry. He never wanted to make Red cry. He loved him. He loved him so much. He only wanted Red to keep smiling, and laughing. That was all. Nothing more.

... If it made Red stop crying, then Sans can promise to give up. He’ll give up loving Red, just to see him smile again.

Sans smiled at the thought, even if his eyes showed melancholy. For Red, he would do that—he would do anything to see him smile and laugh.

Sans carefully moved his hand and gently wiped away the tears. “Don’t cry. I’ll give up. I’ll promise to give up. So don’t cry anymore.”

Somehow, hearing those words broke Red even more, and he became a sobbing mess.

Sans was so gentle and kind, and even now, continuing to coo and promise for him, promises that Sans would be sure to keep if he ever made any ... just as long as Red wouldn’t cry anymore.

It hurt to love. His heart was already crushed twice. He didn’t want to expect anything anymore. Because he was just so tired.

... But for Sans. 

Red gazed at the large troubled skeleton. He would’ve laughed with how much the other was doing his best to calm him down; to make him happy ... forgoing of his own as if Sans’ happiness never mattered.

But it did.

Red loved it when Sans smiled and laughed just as much. To see the ... unhindered fondness and affection of those gazes. The warmth and ... love in them.

Red found himself smiling warmly, leaning into the large hand wiping his tears away.

_... For the third time._

Red muttered to himself. “And for the last time.”

For Sans ... It would be worth it.

“... Y-You don’t have to p-promise.” Red wanted to blanch when his voice cracked and became hoarse from his sobbing. But he continued on, his small hand held the back of the large one on his face, whilst his other continue to hold onto the other’s chest. “I ... I l-like you too.”

Red ignored the heat rushing in, colouring his entire face as he continued to gaze at Sans warmly—encouragingly.

Sans’ soul shook. He couldn’t believe what he heard. “R-Red. A-Are you—” he gulped, attempting to calm his also quaking hand that Red held. “Are you s-sure? I don’t want to hurt you. Y-You’re so precious to me.”

“Yeah?” Red smiled, his heart swelling with unbounded happiness that it had to be illegal to feel such a thing.

“Yes.” Sans said firmly, hiding nothing. Red felt like crying again from the sheer pureness of the sincerity. “I love your laughs and smiles. I love how passionate you are. I love how protective and caring you are about friends and family.” Sans didn’t realize that he was crying until his vision of Red blurred, but still he continued. “S-smart, funny, ama-azing, sweet.”

Sans hiccupped and sobbed, unable to hold himself back. “I-I love you. _Hic_. ‘M sorry. Sorry Red. Love y-you so- _hic_ -much. S-Sorry.”

“Hey, hey,” Red tiptoed, and seeing this, Sans subconsciously aided the small skeleton by lifting him up with his arm. Red was seated on Sans’ forearm as he reached to cup the other’s face, wiping at the tears. “It’s okay, Sans. Shhh. It’s okay. Didn’t I say that liked you too?”

“B-But that’s—”

“Shhh.” Red placed both hands on Sans’ mouth. Then, he slowly removed them when he was sure that Sans was going to let him speak and placed them back on the other’s cheeks; gently caressing the wet bones.

“I ... I was scared. And no, not because I didn’t like you.” Red pecked Sans’ nose. “I’m telling you now, I like you a lot more than you think.” He made sure to look at Sans when he said that, before he looked down as he took a deep breath. “I just ... had a bad time with the whole relationship thing. It ... It hurt a lot. That’s why I was really scared Sans.”

Red looked up to meet Sans’ gaze. “I was scared, and I didn’t want to hurt anymore. But I-I—” Red inwardly cursed, trying to control himself to not start bawling again. He refused to cry so much in one day. Plus, Sans was already crying enough for the both of them. It took a moment before he continued. “... I fell for you too.”

Red heard and _felt_ Sans take in a breath. “That’s right you ... big oaf! Look at what you’ve done. Making me feel ... _feelings!”_

Sans let out a choked laugh that made Red smile. The small skeleton poked the other’s nose accusingly. “Shame on you, Sans. I lost a lot of sleep thinking about your cute as hell face.” Red crossed his arms, and then stomped for an added effect in relaying his _frustrations._ “Y-You better take responsibility!”

“Y-Yes sir. Hehe. Stars. I’m so happy. So happy, Red. Thank you. This is t-the best day of my life.”

Red flushed, muttering. “Y-You don’t have to be _that_ happy.”

Both skeletons were startled when the power surged back; the lights turned on, and the elevator began to move again.

“Geez, took their damn time fixing the fucking thing.” Red made sure to wipe the leftover residue of his tears, and then went to help Sans with wiping his own face. At the very least they should look ... presentable enough. The destroyed shirt was a lost cause though.

Once done, the small skeleton huffed. “We need to get Alphys. She may have a way to get you back.”

Sans simply hummed, but now wore a big smile on his face. Red thought that it looked dumb. Definitely not cute or endearing whatsoever.

“Hmph. Even if she can’t help you out now, we are totally still getting dunchers.”

Sans snorted. “Dunchers.”

Red nodded solemnly. “Dunchers.”

Both shared a moment of silence, before they burst out laughing at the stupid name they made up.

And all the while, Red couldn’t help but think that this time, loving someone didn’t need to hurt anymore.

**Author's Note:**

> Worked on this for the past two days. XD
> 
> I didn't mean for it to get this long, but it happened. Oh well. :3
> 
> Hope you like it Ryu~!


End file.
